Breast Cancer and Pesticides

Transcript

The link between pesticides and breast cancer is controversial, and one person who believes that it's real is Professor Mary Wolff of Mount Sinai Medical Center in New York.

She's been researching this field for some years, and is no stranger to the controversy.

Mary Wolff: We knew from Silent Spring, the effects of DDT on reproductive function, especially in birds, where their eggs were no good, and in the early '80s there was one observation in humans that piqued my interest. That was that women with high levels of DDT in North Carolina had a shorter duration of lactation, something we thought was a hormonal effect.

Norman Swan: What sort of hormonal effect does DDT have?

Mary Wolff: DDT acts like oestrogen in certain test systems.

Norman Swan: So this is what some people think has called the feminisation of alligators in Florida, and maybe reduced sperm counts in men and so on and so forth; it's that whole synthetic oestrogen story?

Mary Wolff: That's right, and because we know that oestrogen is strongly related to breast cancer risk, that connection caused us to want to look further.

Norman Swan: You did what's called a case control study. You compared women with breast cancer with women who didn't, and looked at various factors including their exposure to pesticides.

Mary Wolff: That's right. My collaborators at NYU Paolo Toniolo had a group of 14,000 women on whom he had drawn blood at one time point, and then followed them until they got cancer, and then compared them to other women in a cohort who don't have cancer.

Norman Swan: And what were the findings?

Mary Wolff: In the initial study we did, we found that women with the highest 10% of DDT levels had about a fourfold increased risk of breast cancer, over women with the lowest 10% of DDT levels.

Norman Swan: Did you measure other synthetic chemicals as well?

Mary Wolff: We did. In that study we also looked at PCBs and we did not see a significant effect.

Norman Swan: Have other people tried to replicate them - what have they found?

Mary Wolff: There are more than 30 studies worldwide going on to look at the issue of pesticides and breast cancer, and some of them have been positive and some of them have been negative. Not all of the big studies have yet been published however.

Norman Swan: Why should it be that a synthetic oestrogen, or a synthetic chemical that has oestrogenic effects causes this problem when the oestrogenic effects for instance of soy are thought to be protective? Why do you get one chemical producing the problem which just happens to be synthetic that may increase the risk of cancer, when a natural vegetable form prevents it?

Mary Wolff: What we find is that effects on oestrogen receptive. For example, a multiple tamoxifen can be both oestrogenic and anti-oestrogenic.

Norman Swan: Tamoxifen is a drug they use after breast cancer.

Mary Wolff: That's right. And indeed the same thing is true of this compound genistein and is in soy. At certain dose levels it can be oestrogenic and at higher doses it can be anti-oestrogenic, and in fact in animal studies you can find that it has a protective effect under many circumstances, both for breast and prostate cancer.

Norman Swan: Is there corroboratory evidence that suggests that DDT phenomenon might well be a real phenomenon? In other words, has there been a rise in breast cancer through the years that DDT's been used - you know, can you sheet it home through more than one source than just your case control study?

Mary Wolff: It's hard to say. The fact is that breast cancer's been going up ever since society became westernised, and breast cancer risk is much higher in western countries. And much of the recent rise in breast cancer incidence parallels the use of DDT. But of course that kind of association means very little.

Norman Swan: So video tape recorders went up at the same time as HIV came along.

Mary Wolff: I say roller skates, same thing! Exactly the same thing. But my view is that even if DDT exposure turns out to be a risk factor for breast cancer, it's not going to be a risk factor for everyone, and certainly in the United States in many western countries, it's not going to be a risk factor much longer because it's no longer in the environment at a detectable level.

Norman Swan: There is a significant gap in our knowledge in terms of risk factors for breast cancer. What's the extent of our ignorance?

Mary Wolff: Well that again is something that has really propelled in a recent interest in looking at environmental exposures in breast cancer. That is that at most studies that try to explain breast cancer risk, come up with about 40% or 45% of risk, and most people think it's lower than that and it's like 30%. Most women who get breast cancer do not have any of the major risk factors. The major risk factors for breast cancer are age, country of birth, and family history. We also know that reproductive history - the time at which you get your first menstrual period and the time at which you have your first child, and the age of menopause, are important. And those are the big risk factors. All those together don't explain all breast cancer risk, and most women who get breast cancer have none of those risks.

Norman Swan: What's your guess as to the attribution of environmental factors?

Mary Wolff: My guess is that in some certain sub-groups of women who are susceptible or who were exposed at a very sensitive period of breast development, may have increased risk due to pesticides or to other environmental factors.

Norman Swan: Is there any evidence that women who live in the country rather than live in cities, are more at risk of breast cancer?

Mary Wolff: No, quite the opposite. The more urbanised the society the more breast cancer risk.

Norman Swan: And how does that tie in with the DDT levels?

Mary Wolff: Well actually we just did a study in Vietnam where the levels among urban women were much, much higher than the levels of rural women. It could be that women who live in cities have more money and can buy more meat, and more milk.

Norman Swan: Could this be a problem that started in childhood and has an influence on female puberty rather than an influence later in life on women's breast tissue?

Mary Wolff: It could possibly be, and that's something that's really an interesting area to study. Some people believe that exposures around birth may be responsible for some of breast cancer risk.

Norman Swan: Mary Wolff is Professor of Community Medicine at Mount Sinai Medical Center in New York.